OSU plant pathologist Dr. Sally Miller has reported that on May 20, 2010 Penn State announced that late blight was confirmed on locally grown greenhouse tomato transplants in northwestern PA.  This follows reports of outbreaks in Louisiana, Florida and Maryland.   The symptomatic plants in Pennsylvania have been destroyed and the grower has adopted a fungicide spray program to manage the disease.  The inoculum source has not been identified.  The Pennsylvania Department of Agriculture has been screening tomato transplants received for wholesale and retail markets in the state and so far none have been identified as having late blight.

Given the cool and rainy weather conditions of the past several weeks, which favor late blight, it is a good idea for growers and gardeners alike to be aware of the potential for the disease to occur in Ohio this year.  Late blight does not survive the winter in Ohio unless it is protected in living plant tissue.  A possible source of inoculum at this time of year is volunteer potato plants that were infected last season.  Volunteer potatoes should be destroyed as soon as they emerge, particularly if late blight was observed in the area last year.  Gardeners should watch the space where potatoes were planted last year and remove and destroy any potato plants that emerge.  Commercial growers planting corn after potatoes may consider several herbicide options as described in this linked article from Michigan State University.

When purchasing potato seed or tomato transplants, growers and gardeners alike should inspect the planting material carefully and reject any with disease symptoms.  Fungicides are available for management of late blight but in general must be applied before the disease appears.  For gardeners, products containing the active ingredient chlorothalanil are recommended.  Read the label carefully and apply the fungicide according to label requirements.  Commercial growers have a number of products available to them.  Tomato late blight management recommendations for gardeners and growers (conventional and organic) are available in OSU's newsletter VegNet 16(14), June 25, 2009, linked here.

Find a June 2 late blight update from OSU Extension linked here.